Doppler Echocardiography

Abstract

Aortic stenosis is one of the most common cardiac valve disease and can lead to death and different other morbidities. Doppler Echocardiography is the important diagnostic tool for the evaluation of different cardiac conditions including aortic stenosis. It is a safe and key non-invasive imaging technique for hemodynamic assessment as well as of aortic valves and stenosis. By the help of continuous-wave, pulse-wave and colour Doppler diagnosis can be made and also optimization and monitoring of therapy can be carried out accurately. The paper focuses on the use of a non-invasive imaging approach in assessment of cardiac valves of an old aged patient with different co-morbidities and aortic stenosis in particular.

Keywords: Doppler echocardiography, continuous-wave Doppler, pulse-wave Doppler, Aortic stenosis, Heart.

 Introduction

Cardiac valve diseases are quite frequently presented, however their clinical course and management is still challenging and therefore demands accurate information regarding severity of valve damage, heart function and patient symptoms. Aortic stenosis is mainly due to age-related degenerative disease and is characterised by shortness of breath with activity and chest pain (Carita et al, 2016). In view of the number of co-morbidities including cardiac issues, the morphology of the different cardiac valves and the velocity of blood flow within them is necessary to determine. In order to do so great deals of diagnostic techniques have emerged and they are offering valuable benefits. Early intervention of the valve disease can prevent valve replacement/ implantation surgeries and poor prognosis (Everett et al, 2018).  Doppler echocardiography is one of the latest non-invasive techniques that have acquired a central place in the cardiovascular ultrasound assessment. It illustrates hemodynamic status corresponding to the tomographic anatomy (Płonska-Gosciniak et al, 2019).  This paper aims to review the role of Doppler echocardiography (including both pulse-wave and continuous wave Doppler) in the non-invasive detection of cardiac abnormalities.

Case

A 80-year-old woman with osteoarthritis and type II diabetes and hypertension presented with self-resolving chest tightness while making the bed. She had a background of bilateral knee replacements and closure of cerebral AV malformation. She had an atonic bladder which required self-catheterisation. She had previously had an echocardiogram demonstrating mild aortic stenosis. She stopped smoking about 15 years ago.

Before the patient’s episode about 6 weeks ago, she reported strange sensations in the chest with something apparently moving. This could possibly be a sort of palpitation or apprehension. Whilst she did describe a degree of exertional tiredness there had been no convincing recurrence of the chest discomfort. She had no claudication as well.

She was on Amlodipine 10mgs, Atorvastatin 20mgs, Citalopram 10mgs, Empagliflozin 10mgs, Ferrous Fumarate 305mgs, Gliclazide 80mgs, Lansoprazole 30mgs, Loratadine 10mgs, Perindopril 4mgs, Sitagliptin, Naproxen, and Paracetamol. Whilst she was not allergic to any definite medications she was allergic to Ibuprofen, Codeine and also fish.

Her ECG showed sinus rhythm with normal axis, normal PR, QRS and QTC interval. There were no pathological Q waves. There was a non-specific ST flattening in V6, AVL and lead I. No evidence of ischemia was found on ECG.

Her BP was 141/81 and pulse 71bpm regular. She had an ejection systolic murmur over the aortic region with an audible second heart sound and no clinical aortic regurgitation. The JVP was not raised, there was no oedema and the chest was clear.

The ejection systolic murmur and symptoms of this patient are consistent with the existence of aortic stenosis (Thomas and Makaryus, 2019).  Aortic stenosis is a condition characterised by reduction in the size of aortic valve orifice owing to the malfunction of the aortic valve leaflets. They fail to open completely during systole with resultant increase in after load and hypertrophy of left ventricle (Carita et al, 2016). The characteristic triad of symptoms of this condition are dyspnea, angina and syncope.

Aortic stenosis is commonly seen in older people age above 60 years due to senile degeneration or aortic valve calcification (Fattouch, Castrovinci and Carità, 2016).  Although, exact cause not known, it is believed that turbulence and high pressures over many years lead to the endothelial damage, lipid penetration, and an inflammatory condition that causes infiltration of T lymphocytes and macrophages. This further initiates the thickening and fibrosis of leaflet and ultimately calcification (Dweck, Boon and Newby, 2012).

Once symptoms of aortic stenosis develop, the prognosis becomes poor while at present, there is no medical treatment to prevent the disease. The mainstay of treatment is surgical valve replacement (Fattouch, Castrovinci and Carità, 2016). Hence, it is of prime significance to delineate and recognize the crucial basic mechanisms and heart’s anatomy.

In this particular case in order to gain a better understanding of the function, hemodynamic and structure of the heart and considering the patient’s condition, the help of Doppler echocardiography was taken. It offers precise estimation of severity of valve disease and any cardiac dysfunction (Gaspar, Azevedo, and Roncon-Albuquerque, 2018). It provides an accurate assessment of hemodyanamic function of the heart as well as quantification of both diastolic and systolic via tissue doppler and blood pool. By the help of it valve areas, shunt volume, pressure gradients, regurgitant volume and intracardiac pressures are easily evaluated (Anavekar and Oh, 2009).

In this case using continuous-wave, pulse-wave and colour Doppler echocardiography a number of images were obtained as shown below.

Figure 1: Continuous wave doppler ultrasound showing anterograde and retrograde blood flow.

Figure 1 is an image obtained via continuous wave doppler ultrasound and it shows anterograde and retrograde blood flow. In case of a suspected aortic stenosis, a high velocity flow of blood should be observed across the aortic valve. The figure above demonstrates the line of cursor of the continuous wave Doppler going by the aortic valve in the chamber view. The inferior segment illustrates the tongue like Doppler signal as a result of systolic blood flow in the aorta ahead of the aortic valve.  The scale underneath shows the time axis while the velocity is represented by the vertical scale. The jet of velocity here is a little high, almost 3 m/s, pointing to moderate aortic stenosis.

Figure 2: Pulsed wave Doppler at the LVOT

This is an image obtained through pulsed wave Doppler ultrasound at the left ventricular outflow tract (LVOT) (figure 2). The velocities are plotted in the y axis and time is plotted on the x axis. All velocities are plotted as one yellow point comprising a decent flow profile. The image shows more intensity of the density of yellow points which means signal coming back to the probe is stronger at the velocity/frequency (Anavekar and Oh, 2009).

The green line demonstrates the baseline and point below this line are velocities moving away from the transducer. On the other hand, velocities moving towards the transducer are situated above the green line and represent a pulsatile flow. The velocities are slightly elevated i.e. above 1m/s so Bernoulli equation cannot be considered here and for this reason the aortic valve area (AVA) can be underestimated.

 

Figure 3: Parasternal long axis of the AV demonstrating calcification and cusp excursion

In this figure 3 aortic valves appear to be thick calcified and stenosed since they give the appearance of being brighter on the scan. The thick valves can obstruct blood flow significantly. Calcific aortic valves are also linked to increased stiffness of the leaflet, leading to high pressure gradients across the valves (Saikrishnan et al, 2014). In this particular figure reduced aortic valve excursion can also be observed resulting in diminished aortic cusp separation. Evidence has shown that an aortic cuspal separation points towards the severity of aortic stenosis (Jayaprakash, Dilu and George, 2017). Maximum aortic cuspal separation thus is a useful screening tool for assessing the severity of stenosis especially when there is disagreement among the other parameters of echocardiography.

Additionally, Doppler colour flow mapping also plays a vital role in the precise non-invasive assessment of a number of heart associated haemodynamic disorders (Mitchell et al, 2019). It is especially helpful in detecting regurgitant lesions in cardiac valves. In colour Doppler the direction and mean velocity of blood flow are colour coded in the scan plane and are placed over on to the cross sectional image to create a spatially adjusted map of flow (Temporelli et al, 2010). This is shown below in figure 4.

Figure 4: Parasternal long axis view- colour Doppler demonstrating turbulent flow at valve level

Colour Doppler is used to measure the direction and velocity of blood flow overlay a colour pattern (Anderson, 2017). Conventionally, red colour is the blood flowing towards the transducer while blue colour shows flow moving away from the transducer. The high velocities are illustrated in lighter colours or by altering colour to yellow. In order to appreciate the turbulent flow, a threshold velocity is taken as a reference, above which any change in colour indicates the turbulence (Mitchell et al, 2019). Generally a “mosaic pattern” is regarded as a turbulent flow in colour Doppler ultrasound. Same is the case in figure 4 which shows a mosaic pattern i.e. turbulence at the valve level.

Once disease is established, management depends on its progression. Nevertheless, it is definite that the huge numbers of unfavourable cardiac events take place in patients with symptoms; hence, the common approach is an observant waiting with series of ultrasounds, echocardiograms as well as visits to doctors to evaluate the development of severity (Czarny and Resar, 2014). For this particular case the guidelines suggest that the patients should have a transthoracic Doppler echocardiogram for at least every 1–2 years (Czarny and Resar, 2014). Since this patients have valve calcification and less than 4 m/s peak aortic jet velocity, she should be re-examined every six month. Also, aortic stenosis accompanies with Hypertension may cause further problems, such as it can mainly affect gradients and flow (Mascherbauer et al., 2008). Thus, it needs to be managed medically although medical therapy is inefficient in aortic stenosis.  When aortic stenosis becomes severe, only definitive management for this patient would be transcatheter or surgical aortic valve replacement.

Discussion

The clinical usefulness of Doppler echocardiography for the evaluation of aortic stenosis was discussed in a patient with multiple co-morbidities.  A precise assessment of the severity of aortic stenosis is essential for risk stratification and patient treatment as well as to assign symptoms rightfully to the valvular disease (Baumgartner et al, 2009). Doppler echocardiography not only helps to examine the severity of this disease but also takes part in the therapeutic management of aortic stenosis (Feigenbaum, Armstrong and Ryan, 2010). It gives insight into the morphology of the aortic valve. Nevertheless, there are other modalities as well in addition to Doppler, for instant, cardiac catheterisation, magnetic resonance imaging (MRI), and computerized tomography (CT) scan. Cardiac catheterization is conventionally used for definitive examination of valvular heart disease as well as a therapeutic procedure but it’s an invasive procedure (Manda & Baradhi, 2019). For this reason there are chances of certain complications like retroperitoneal bleeding, hematoma, formation of arteriovenous fistula, allergic reactions, stroke, etc. Moreover, cardiac catheterization requires an interventional cardiologist, radiologic technologists and nurses to perform it whereas for doppler echocardiography sonologist is enough (Otto, 2018). Yet, cardiac catheterisation can remove discrepancy in echo diagnosis (Saikrishnan et al, 2014). Besides, studies have also found echocardiography equally reliable to magnetic resonance imaging (MRI) in assessing aortic stenosis (Wong, 2016). Nonetheless, MRI offers greater sensitivity and specificity in the detection of severe aortic stenosis and also provides three-dimensional anatomy (Mathew et al, 2018).

Doppler echocardiography allows seeing the calcification and thickening of valve and valve mobility as does the cardiac catheterization. It can help differentiate the congenital anomalies with the acquired one (Otto, 2018). The major principle of Doppler echocardiography is that it uses ultrasound to trace flow of blood in the vascular and cardiac system (Kisslo, and Adams, NA). The alterations in the frequency of the signals coming back from tiny moving targets such as red blood cells are caught by the ultrasound beam. These moving targets cause the ultrasound beam to move back to the transducer. When these targets move towards the transducer, the higher frequency is detected and when they move away from the transducer the lower frequency is detected (Oh, Seward and Tajik. 2007).

In the present paper, for the particular case, cardiac catheterization can cause a number of complications since patient had multiple co-morbidities and had also been operated for AV malformation. Thus, best practice here would be the use of non-invasive Doppler ultrasound. Thus, three different Dopplers were used to find out the pathology and highlighted their importance especially in detecting aortic stenosis and its severity.  Continuous wave Doppler echocardiography has been an established technique in quantitating and observing the blood flow disturbances and high velocity that describes several regurgitant and stenotic valvular problems (Savage and Aronson, 2004). It continuously transmits the Doppler signals toward the red blood cells (RBCs) which are moving and also continuously receives these signals coming back from these RBCs. Its chief advantage is in its capability to show high velocity signals. It can reliably measures any velocity shift and predicts the pressure gradient even in aorta with calcification (Otto, 2018). Continuous wave Doppler can determine the severity of aortic stenosis via modified Bernoulli equation P = 4V² and it measures the mean and the pressure drop all through the valve (Anderson, 2017). In this patient it was not found to be beyond 70 mmHg, thus ruled out severe stenosis.  However, continuous wave has no ability to restrict blood flow velocity measurements (Moorthy, 2002). 

On the other hand, the pulsed wave Doppler sends a solo ultrasound crystal in pulses or short bursts and entertains sound beams. The pulse wave Doppler via range gating can choose Doppler information from any spot within the cardiovascular system consuming a sample volume (Anderson, 2007). It means it can make localized measurements of flow velocity. However, it has a shortcoming in its capacity to quantitate the high velocities. The Doppler equation used to measure these velocities is shown in the figure 5 below.

Figure 5: Doppler formula

The best ultrasound system must demonstrate an ability to carry out continuous wave assessment as well as repetition frequency examination at high pulse in patients with several cardiac issues (Baumgartner et al, 2009). In order to obtain an optimize image an apt transducer, adequate depth and spatial resolution are very essential elements. The dynamic range setting helps to adjust the hues of gray on the image (Mitchell et al, 2019). Non-guided CW (PEDOF) probe is very much required to precisely examine native aortic valve stenosis (Feigenbaum, Armstrong and Ryan, 2010).

In this particular case Doppler ultrasound had helped to locate and assess the primary lesion. Continuous wave doppler ultrasound showed high jet velocities (> 1.5m/s) demonstrating the presence of moderate aortic stenosis while pulse-wave showed slow velocity i.e. <1.5m/s. Colour Doppler illustrated the presence of turbulent flow across the valve.

Overall, all these findings were suggestive of ‘moderate’ aortic stenosis. In order to get more precise information nuclear imaging, CT scan and MRI are recommended (Czarny and Resar, 2014).

 

Conclusion

Using Doppler echocardiographic that provides objective information on the cardiac valves, clinicians can not only diagnose the disease but also they can recommend treatment options and requirement for valve replacement.